The Population Studies Center (PSC) at the University of Pennsylvania (Penn) has fostered research and training in population since 1962, with NICHD infrastructure support since 1978. Our goal is to remain a national and world leader in research on the growth and structure of human populations and the population perspective on health; and in the development of populations scientists, especially those grounded in demography. The PSC is characterized by remarkable continuity in its production of high-quality research bearing directly on the major themes of the DBSB: demography, behavioral and social science approaches to sexually transmitted diseases and reproductive health, and population-based studies of health and human development. This application is for the continuation of a co-ordination infrastructure that will: 1. Support the production of innovative, high-quality research on human populations -- the determinants and consequences of their structure and organization, their dynamics, and their health and well-being. Our emphasis is on: a) the study of the social and behavioral bases of health, including their interaction with health care policy, the implementation of health programs, and the distribution of social and economic resources. b) a population perspective for undertaking and evaluating interventions related to human capital development with sensitivity to underlying behaviors and endowments. c) demographic concepts and methods as important frames for interpreting the aggregation of diffuse individual characteristics; for the treatment of heterogeneity in human populations; and for the distribution of human capital (including health) and social status across generations. 2. Maintain an adaptive PSC at Penn that continues to facilitate and promote innovative, long-term careers for participating research scientists with a focus on providing opportunities for interdisciplinary research, and targeted development of junior faculty towards careers as influential population scientists. 3. Be an efficient conduit for application of scientific analyses, results, and innovations and the exchange of the human capital and organizational resources embodied in the PSC through engagement and evaluation of policies for the betterment of health; and co-ordination of research and scientific exchange between the population-based social sciences and the medical sciences research communities within Penn, across US and international population research centers.